Key reaction steps and active surface phase of vanadyl pyrophosphate for selective oxidation of butane

Abstract

Among several crystalline V-P oxides, (VO) 2P 2O 7 was the most selective for maleic anhydride production from butane oxidation. This is because (VO) 2P 2O 7 was selective In the key step of the oxidation, i.e., the dehydrogenation of butane to butene. Effect of microstructure (shape and size of catalyst particle) was studied using (VO) 2P 2O 7 prepared with four different methods. Phenomenologically, the microstructure had a great influence on the selectivity especially at high conversions; a plate-like particle was more selective than a particle having rose-like shape. Over the former catalyst, the consecutive oxidation of product maleic anhydride was much slower, resulting in the high selectivity at high conversions. The surface P/V ratios of these (VO) 2P 2O 7 were determined to be close to that of the bulk (P/V = 1) by XPS with V-P-O glasses as standard materials, suggesting that the active sites are (V 4+=O)-O-V 4+ pair sites on (100) plane. By isotopic studies, e.g., butane + 18O 2, it was revealed that reduction-oxidation only near the surface was involved in the catalysis.